A variety of pressure transducers have been developed heretofore for various applications. Many such transducers incorporate a pressure sensitive silicon die having piezoresistive elements on one side thereof which generate corresponding electrical signals upon flexure of the die in response to pressure. Proper mounting of the pressure sensitive silicon die is crucial to performance of the transducer.
One such type of transducer is the so-called "wet-to-wet" pressure transducer wherein the die serves as a diaphragm between two fluid pressure media in direct contact therewith. Such transducers are used in various medical and automotive applications, vending machines, etc. In pressure transducers of this type, the die must be mounted in a way which not only provides the necessary mechanical support, but which also provides a fluid-tight seal in accordance with the particular application. Since the die is in direct contact with the fluid media, a protective coating is often provided which can affect sensitivity and repeatability. Consequently, for best performance it is especially desirable to mount the die in a manner which minimizes extraneous stresses thereon while satisfying the necessary mechanical supporting and fluid-sealing requirements.
Pressure transducers with elastomeric mounts have also been available heretofore. For example, U.S. Pat. No. 4,656,454 to Rosenberger, which is assigned to Honeywell Inc., the assignee hereof, shows a wet-to-wet pressure sensor wherein the die is clamped between premolded elastomeric ring seals seated in opposing portions of a housing. Although this pressure transducer performs quite well, there are some drawbacks to the particular type of mounting utilized therein. The silicon die is under continuous stress which interferes with sensitivity. Small manufacturing variations in the premolded elastomeric seals and/or variations in assembly of the package can induce additional stresses which can affect proper fluid sealing and further interfere with sensitivity. Also, the configuration of the mounting virtually requires the use of a protective coating on the exposed circuitry elements of die which in turn increases hysteresis effects, reducing repeatability and performance. U.S. Pat. Nos. 4,665,754 to Glenn, 4,658,651 to Le, and 4,373,397 to Keller are also representative of the prior art in this regard.
A need has thus arisen for an improved wet-to-wet pressure sensor having a better elastomeric mounting which satisfies the necessary fluid-sealing requirements while at the same time avoiding unnecessary stresses on the die and protecting exposed circuit elements from corrosion by the contacting fluid media in order to achieve better sensitivity and performance.